This invention is for a unique prefabricated storage building in which all of the components are interlocked without the use of fasteners. The building is intended primarily for use by the military for ammunition storage and is designed to withstand high forces applied both from within the building and from without. Provisions are included for covering the structure with earth to provide the building with additional integrity and security. The building can be erected on a prepared site within a matter of a few days, whereas erection time for previous designs for similar uses was measured in months, and at much higher costs. While the disclosed modular storage building is intended for storage of munitions, it is useful for general storage when military security is important.